1. Field of the Invention
The present invention relates to a lens, and more particularly, to a projection lens.
2. Description of Related Art
Most projection apparatus utilizes an optical engine to convert a light beam emitted from a light source into an image and projects the image beam onto a screen through a projection lens so as to display an image. Therefore, the quality of the projected image from a projection apparatus is closely related to the optical engine and the projection lens.
FIGS. 1A and 1B are perspective view of a camera lens assembly 100 disclosed in R.O.C patent No. 1236573. The camera lens assembly 100 includes a bracket 110, a zooming ring 120, a front sleeve 130, a lens 140 and an elastic component 150. The bracket 110 has a plurality of inclined grooves 112 and a plurality of hook arms 114. The zooming ring 120 has a plurality of protrusions 122 and an inner spiral 124. The front sleeve 130 has an outer spiral 132. When the zooming ring 120 is assembled to the bracket 110, each protrusion 122 of the zooming ring 120 is located inside one of the inclined grooves 112 of the bracket 110. After engaging the outer spiral 132 of the front sleeve 130 to the inner spiral 124 of the zooming ring 120, the front sleeve 130 is accommodated inside the zooming ring 120. Furthermore, the lens 140 is disposed inside the front sleeve 130. The elastic component 150 is pressed against the front sleeve 130 and the hook arms 114 of the bracket 110 hook onto the elastic component 150.
As shown in FIG. 1B, when the protrusions 122 of the zooming ring 120 slide along the inclined groove 112, the zooming ring 120 rotates relative to the bracket 110. During the duration of rotation, the zooming ring 120 moves up or down to adjust the focus of the camera lens assembly 100.
However, the camera lens assembly 100 is mainly designed for a camera. If we want to apply the camera lens assembly 100 to a projection apparatus having aspherical lens, because the front sleeve 130 incorporating the aspherical lens rotates synchronously with the movement of the front sleeve 130 in the axial direction, the quality of image projected from the projection apparatus is compromised. To prevent the deterioration of the image quality from a projection apparatus due to the rotation of the aspherical lens, a projection lens with a non-rotational front sleeve is proposed. FIG. 2 is an explosion view showing the major components of a conventional projection lens.
As shown in FIG. 2, the conventional projection lens 200 includes a front sleeve 210, a rear sleeve 220, a main sleeve 230, a metal ring 240, a plurality of lenses 250, an adjusting rod 260, three screws 270 and anther three screws 280. The front sleeve 210 has three threaded holes 212, the rear sleeve 220 has one threaded hole 222. The main sleeve 230 has a straight groove 232, three threaded holes 234 and three grooves 236. The metal ring 240 has three lateral grooves 242 and three inclined grooves 244. The lenses 250 are disposed inside the front sleeve 210 and the rear sleeve 220 respectively.
The main sleeve 230 covers the front sleeve 210 and the groove 236 exposes the threaded hole 212. The main sleeve 230 also covers the rear sleeve 220 and a part of the rear sleeve 220 exposes outside the main sleeve 230. The straight groove 232 exposes the threaded hole 222. The adjusting rod 260 penetrates through the straight groove 232 and locks inside the threaded hole 222. The metal ring 240 connects with the main sleeve 230 and the front sleeve 210. The lateral groove 242 exposes the threaded holes 234. The three screws 270 penetrate through the lateral groove 242 and lock inside the threaded holes 234. The inclined grooves 244 expose the grooves 236 and the threaded holes 212. Therefore, each screw 280 penetrates through one of the inclined grooves 244 and the grooves 236 and locks inside one of the threaded holes 212.
The direction of extension of the grooves 236 of the main sleeve 230 is parallel to an axis A of the main sleeve 230, the screws 280 is constrained by the grooves 236. Therefore, when the metal ring 240 rotates, the front sleeve 210 is only pushed along the axis A of the main sleeve 230 without rotating the front tube 210. As a result, the projection apparatus can project a clear image on a screen. However, the projection lens 200 uses a total of 7 locking elements (the adjusting rod 260, the three screws 270 and the three screws 280) for the assembly so that considerable time and cost is wasted in assembling the projection lens 200. Moreover, most manufacturers prefer to engage the screws 270, 280 with a sleeve for providing a better locking effect. Consequently, the assembling process is even longer and the cost of producing the projection lens 200 is even higher.
Furthermore, the presence of the lateral grooves 242 and the inclined grooves 244 on the metal ring 240 demands the metal ring 240 to be fabricated using a metal with a higher mechanical strength to reduce the degree of deformation when the metal ring 240 is worked on. However, the selection of a high-strength metal will increase the production cost.
Because a total of 6 grooves are formed on the metal ring 240, deformation problem is a still a major concern even if a high-strength metal is used to fabricate the metal ring 240. Moreover, the sharp edges of the lateral grooves 242 and the inclined grooves 244 often prevent the metal ring 240 from rotating smoothly after the metal ring 240 is assembled to the main sleeve 230. In addition, the metal ring 240 may scratch the surface of the main sleeve 230 causing surface abrasion of the main sleeve 230.